This specification will at times refer to "layered silicates." The layered silicates to which the invention is applicable are of the type which can be represented by the general formula E.sub.i M.sub.x Si.sub.y O.sub.n (OH).sub.m where M is A1, Mg, or Fe, x=2 to 6; y=2 to 8, n =2 to 20, m=0 to 8, and E.sub.i is one or more exchangeable ions (K, Na, Mg, Ca, Ba, Fe, Li, etc.). These layered silicates will hereinafter in this specification be referred to as "layered lattice silicates".
It has been recognized that the surface treatment of substrates of the mineral or clay mineral type can be enhanced by carrying out the treatment with the use of hydrogen.
In one aspect, the reactants include organic compounds, polymer-forming compounds and the like and the reaction is carried out in the presence of hydrogen which activates or promotes the reaction, at elevated temperatures.
Since the reaction need only take place to a limited extent, viz., at the surface, without involving the bulk of the substrate, thus without problems of diffusion of reactants through already formed surface layers, such processes offer advantages in minimal consumption of materials and energy and in short reaction times as well as in providing a wide variety of structures at the surface. The products have advantages in possessing chemically modified surface properties making them useful for particular applications while retaining desirable physical properties of the bulk of the substrate.
Thus the surface treatment of a clay mineral such as kaolin with a polymerizable substance such as a nylon precursor may be carried out in the presence of hydrogen at elevated temperatures to form a polymer in situ at the surface of the kaolin, the product being useful as a filler in resins, elastomers and the like. Such a product is particularly advantageous as a filler in a matrix with which the treated kaolin surface is compatible or to which it is similar whereby better adhesion is achieved between the two.
It has also been recognized that a layered lattice silicate may be surface modified by a gas which enters directly into the reaction, e.g., NH.sub.3.
In this disclosure the term "surface modified" means that only the surface of the substrate is modified and no breakdown of its structure other than that normally associated with heating in the range set forth herein, occurs.
In my U.S. Pat. No. 4,764,495, issued Aug. 16, 1988, there is disclosed a method for producing a layered lattice silicate which is surface modified with an organic material, by pretreating the silicate such as a kaolin in a hydrogen atmosphere, and then reacting the product with a suitable organic compound.
In my application U.S. Ser. No. 943,669, filed Dec. 17, 1986, U.S. Pat. No. 4,789,403, issued Dec. 6, 1988, there is disclosed a method for producing a layered lattice silicate which is surface modified with an organic material, by contacting the silicate such as a kaolin with an organic monomer, comonomers, or a prepolymer, and effecting surface polymerization or reaction in situ in the presence of a gaseous hydrogen atmosphere. It is believed that the polyamide (nylon) type polymers grow from the surface of the mineral which results from the exposure of the mineral surface to nylon type monomers/prepolymers; and that in the case of the other resins (ABS prepolymer, polybutadiene, polypropylene, polyethylene) the polymer resin is exposed to the mineral surface and becomes bonded to it.
In my copending application Ser. No. 175,868, U.S. Pat. No. 4,859,718, issued Aug. 22, 1989, there is disclosed a method for surface modifying with an organic material a carbonate such as calcium carbonate, which during processing has become coated with processing chemicals, wherein the carbonate in substantially dry, particulate form is contacted with an organic monomer, comonomers or a prepolymer, in the presence of gaseous hydrogen and a calcined kaolin or TiO.sub.2 as a polymerization initiation catalyst.
My U.S. Pat. No. 4,690,868 teaches directly aminating the surface of a 2-dimensional layered lattice silicate comprising reacting the lattice silicate in particulate form with gaseous NH.sub.3 at temperatures below 1000.degree. C. to form bound NH.sub.2 groups at the surface; the resulting modified 2-dimensional layered lattice silicate and a filled resin system employing the thusly modified silicate.
In may application U.S. Ser. No. 089,510, filed Aug. 26, 1987, U.S. Pat. No. 4,798,766, issued Jan. 17, 1989, a method is described for producing a layered lattice silicate which is surface modified with an organic material, which comprises reacting a layered lattice silicate in particulate form with a reactant system comprising gaseous NH.sub.3 at temperatures below about 1000.degree. C. to form bound NH.sub.2 groups at said surface, and reacting the aminated silicate in particulate form in the presence of gaseous hydrogen with an organic compound selected from the class consisting of monomers, comonomers, and prepolymers, which are condensible with the amine group.
An object of this invention is to make improvements in the surface treatment of minerals in the presence of an activating or promoter gas.